1. Field of the Invention
The present invention relates generally to a capacitive type filling measuring apparatus for determining the quantity of fuel or other liquid medium remaining in the fuel tank of a vehicle or the like, and more specifically to an improved arrangement wherein the compensation or reference electrodes which sense the actual dielectric constant of the fuel (or liquid medium) are arranged to eliminate any erroneous indications by the apparatus due to the presence of water or other impurities in the fuel.
2. Description of the Prior Art
In previously proposed arrangements it has been proposed to place a set of reference or compensation electrodes near the bottom of a fuel tank in order to ascertain the dielectric constant of the fuel within the tank so that the output of fuel level sensing electrodes can be modified to allow for the inevitable variations in said dielectric constant of the fuel. However, such an arrangement suffers from the drawback that water or other foreign matter tends to infiltrate in between the plates or electrodes of the reference sensor causing the same to output an erroneous indication of the dielectric constant of the fuel. Water in particular is apt to stay between the plates despite the sloshing of the fuel within the tank, as water has a surface tension about three times that of gasoline. In order to remove this water (or the like) it is usually necessary to remove the reference electrodes and to clean the same using compressed air or the like. Moreover, should the fuel in the tank separate into layers such as is apt to occur when the tank is filled with so called "gasohol" (gasoline-alcohol mixture), or should an excessive amount of water collect in said tank, the output of the reference electrodes is indicative of the dielectric constant of the lower layer only and once again leads to erroneous indications of the fuel volume.